Filtering on multi-valued annotation with 'null' and one other values gives error

[Nicklas Nordborg]

1. Create a string annotation type for samples (or any other item) and set multiplicity to '0'.
2. Go to the list page and configure it so that the annotation type is visible.
3. Add a filter with one value and null (eg. =foo|)

An error message is displayed and the filter is ignored:

Could not filter on 'Sample.#754592': null

The log file has a stack trace with more information:

09:43:44,221  WARN Application:1358 - Could not filter on 'Sample.#754592'
java.lang.NullPointerException
  at net.sf.basedb.core.AnnotationSimpleRestriction.<init>(AnnotationSimpleRestriction.java:163)
  at net.sf.basedb.core.PropertyFilter.getRestriction(PropertyFilter.java:557)
  at net.sf.basedb.core.ItemContext.configureQuery(ItemContext.java:1330)
  at net.sf.basedb.clients.web.Base.getConfiguredQuery(Base.java:953)
  at org.apache.jsp.biomaterials.samples.list_005fsamples_jsp._jspService(list_005fsamples_jsp.java:367)
...

[Nicklas Nordborg]

(In [6832]) Fixes #1934: Filtering on multi-valued annotation with 'null' and one other values gives error

This also fixes the problem with null searches for annotations as outlined in #1205. Though, in this case it was not really related to three-valued logic used in SQL. Null searches on annotations require different queries than what is used to find specific values and the result is OR-ed together.